Yes, someone impersonating someone else is pretty serious. I don't know if a year in jail is the right sentence; maybe six months in jail? Or a year of community service? In any case, it's not right to impersonate another individual. It does require some kind of punishment to discourage others from doing the same.
Yes, impersonating someone on social media should be illegal, but I do not believe in mandatory sentencing. For there are so many different reasons and therefore consequences of these actions are different. A person who is impersonating someone on social media because they have a crush on someone and is too shy to be themselves should not serve the same penalty as someone who deliberately tries to hurt someone through social media.
If someone is impersonating another person purely for comedy or satirical reasons, then that should not be considered a crime. However, if someone is trying to pass themselves off as another person for gain or profit, or to damage that persons reputation, then that should be considered a crime. But each case should be judged on its merits and the actual harm to the person being impersonated.
No, impersonating someone on social media should not result in a 1-year jail sentence. While it's wrong to impersonate another person on social media, the punishment of a year in prison does not match the crime. If someone is found guilty of impersonation, he should have to recant and pay a fine.